Key TakeawaysU.S. Steel's CEO said the company would have to close plants and might move its headquarters out of Pittsburgh if the Nippon Steel acquisition falls through.David Burritt told the Wall Street Journal the company needs the planned infusion of cash Nippon has promised.Both leading U.S. presidential candidates have said they oppose the acquisition. The CEO of U.S. Steel (X) warned that the company would have to close steel plants and likely move its headquarters from Pittsburgh if the $14.9 billi ...